Various methods of positioning a terminal are considered in 3GPP that is being continuously standardized in the field of mobile communication.
Examples of a representative positioning method includes an OTDOA (Observed Time Difference of Arrival) scheme of positioning a terminal using a difference between arrival times of signals received from adjacent base stations, and an AOA+TA method of positioning a terminal using an AOA (Angle of Arrival) and a TA (Timing Advance) of a signal arriving from a base station. As another method, an A-GNSS (Assisted GNSS) and enhanced cell ID positioning method is defined, and a UTDOA (Uplink Time Difference of Arrival) and RF pattern matching method is expected to be adopted.
First, in the case of the OTDOA scheme, there may be a problem in coordinated multi-point transmission (COMP). A scenario of coordinated multi-point transmission for 3GPP LTE includes a scenario in which a heterogeneous network environment in which all transmission points, including a high power node (HPN; e.g., macro base station) and a number of low power nodes (LPNs; e.g., pico cells or remote radio heads (RRHs) connected to the macro base station) within coverage of the high power node, have the same physical cell IDs (PCIs) is assumed.
In a heterogeneous network environment in which all transmission points have the same PCIs, it may be difficult for a terminal to receive a signal (a positioning reference signal (PRS) or other reference signals) transmitted from a base station and the RRHs and determine its position. That is, since the terminal cannot identify the base station or the RRH from which the received signal has been transmitted, there may be a problem in applying the positioning method of the OTDOA scheme. In the OTDOA scheme, precision is improved as a radius of a cell is smaller, but since all nodes within the coverage use the same PCIs, the radius of the cell becomes equal to that of the macro cell, degrading precision.
Next, a positioning method in a current cellular mobile communication system, an altitude of a base station is not considered and, in most cases, the altitude of the terminal is assumed to be the same as that of a base station, which causes failure of determination of the altitude of the terminal and increase in positioning error.